Who they were
By his own account in his writings, he fought some sixty duels without defeat. The most famous, against Sasaki Kojiro on the islet of Ganryujima, is traditionally dated to 1612, though details vary across sources.
He founded the two-sword style Niten Ichi-ryu.
What they did
In later life he served the Hosokawa lords of Kumamoto. In the cave Reigando he wrote The Book of Five Rings (Gorin no Sho, c. 1643–45), a treatise on strategy still read worldwide — in boardrooms as much as dojos.
He was also an accomplished ink painter.
Legacy
Much of his popular image comes from fiction — Yoshikawa Eiji’s novel “Musashi” and the manga “Vagabond” — so the legend should be taken as legend. He remains the ideal of the perfected solitary swordsman.